The present invention relates to a frequency selective plate that performs high transparency of radio waves and visible rays while reflecting heat rays of solar radiation to provide sufficient heat insulation. This frequency selective plate can be used for architectural and automotive window glasses.
Lately, a windowpane coated with a conductive thin layer or covered with a film including a conductive thin layer has been practically used for the purpose of shielding solar radiation. If such a windowpane is applied to multistoried buildings, the windowpane reflects radio waves of TV frequency range to generate ghost image in TV screen and to degrade receiving satellite broadcasting waves through indoor antenna. Further, if such a windowpane is applied to architectural and automotive windows, this functions to degrade the performance of cellular phones and the gain of an antenna embedded in the window pane. In order to solve these problems, a glass plate coated with a heat-reflecting film is employed to transmit part of visible rays and to decrease the reflection of radio waves. This heat-reflecting film is required to be relatively high in electrical resistance and to be transparent.
Further, Japanese Patent No. 2620456 discloses a method for preventing a radio wave trouble by dividing a length of a conductive film parallel to a field direction of incident radio waves into {fraction (1/20)} the wavelength of the radio wave. However, the former method employing the high-transparent heat-reflecting film may not be sufficient in heat-ray shielding performance, although a glass plate made by the former method prevents the radio wave trouble by decreasing the reflection of radio waves. Further, a glass plate made by the latter method disclosed in Japanese Patent No. 2620456 reflects visible rays and near-infrared rays, since the divided length of the film is greater than the wavelength of the visible ray and near-infrared ray. Therefore, although this glass plate ensures a frequency selective performance having a radio wave transmitting performance and a solar radiation shielding performance, this may not ensure the transparency of visible rays. Additionally, in case of a large window employing a large-size glass plate such as one having 2 mxc3x973 m size, it is necessary to take a very long time for cutting a dielectric film into segments of {fraction (1/20)} satellite broadcasting wavelength of about 25 mm by means of a yttrium-aluminum-garnet (YAG) laser.
Each of Japanese Patent Publications JP-A-2000-281388 and JP-A-2000-344547 discloses a frequency selective plate having a radio wave transparent property. This plate is prepared by the steps of (a) forming an Ag continuous layer on a glass substrate surface; and (b) subjecting the coated glass substrate to a heat treatment, thereby changing the Ag continuous layer to Ag particles. Prior to the step (a), an AlN layer is optionally formed on the glass substrate surface.
Journal of Applied Physics Vol. 84, No. 11, pages 6285-6290 (1998) discloses a silver particle-dispersed AlN film fabricated by heating a film consisting of three layers of AlN, Ag, and AlN.
It is an object of the present invention to provide an improved frequency selective plate having a radio wave transparency.
It is a more specific object of the present invention to provide a frequency selective plate which decreases reflectance of radio waves of particular frequency bands for TV broadcast, satellite broadcast and cellular phone while ensuring solar radiation shielding performance and visual light rays transparency.
According to the present invention, there is provided a frequency selective plate having a radio wave transparent property. This frequency selective plate may be referred to hereinafter as the first frequency selective plate and comprises:
a transparent substrate;
a mixture layer formed on said transparent substrate, said mixture layer comprising a mixture of a metal nitride and Ag; and
Ag particles formed on said mixture layer, said Ag particles being two-dimensionally distributed on said mixture layer and being separated from each other.
According to the present invention, there is provided a first method for producing the frequency selective plate. The first method comprises the steps of:
(a) forming a precursory layer on said transparent substrate, said precursory layer comprising a precursory mixture of said metal nitride and said Ag; and
(b) heating said precursory layer into said mixture layer such that said Ag particles, which originate from said Ag of said precursory layer, are formed on said mixture layer.
According to the present invention, there is provided a second method for producing a frequency selective plate having a radio wave transparent property. The second method comprises the steps of:
(a) forming a first precursory layer on a transparent substrate, said first precursory layer comprising a mixture of a metal nitride and Ag;
(b) forming a second precursory layer on said first precursory layer, said second precursory layer comprising Ag; and
(c) heating said first and second precursory layers into a mixture layer comprising said metal nitride and said Ag such that Ag particles, which originate from said Ag of at least one of said first and second precursory layers, are formed on said mixture layer.
The frequency selective plate produced by the second method may be the same as that produced by the first method. In this case, the mixture layer (originating from the first and second precursory layers) produced by the second method can be the same as the mixture layer (originating from the precursory layer) produced by the first method. Alternatively, the frequency selective plate produced by the second method may be different from that produced by the first method. In this case, the mixture layer produced by the second method can have two layers, that is, first and second mixture layers respectively originating from the first and second precursory layers.